This invention relates to nuclear reactors in which a nuclear fuel assembly is contained in a concrete containment. One example of nuclear reactor of this description is a liquid metal cooled fast reactor. Another is a gas-cooled nuclear reactor of either the fast or thermal variety. In the case of the former, a nuclear fuel assembly is disposed in a liquid metal containing primary vessel which is housed in a concrete containment vault, heat being transferred from the fuel to the liquid metal and from thence to steam generators via intermediate heat exchangers. In the case of the latter, a nuclear fuel assembly is supported within a prestressed concrete pressure vessel and gaseous coolant is circulated between fuel assembly and steam generators to transfer heat thereto. In both cases it is necessary to provide thermal insulation to protect the concrete. In the former example, the concrete of the roof of the vault as well as that of the vault sides and base needs to be protected. In the latter example, the concrete of the roof of the pressure vessel as well as that of the wall and floor, requires protection. This invention is concerned with such roof insulation and not with the insulation of walls or base of concrete vault or pressure vessel as the case may be. Such thermal insulation is generally suspended from the appropriate roof by hangers or tie rods, and various proposals have been made for compensating for the changes in dimensions of the insulation as temperature-dictated expansion and contraction, depending on the state of operation of the reactor, occur. One proposal has been to provide both upper and lower ends of the hangers or tie rods with spherical bearings or seatings, but these are liable to stick and then unacceptable straining of insulation and/or hangers or tie rods can occur which can result in insulation becoming detached from the roof.
It is an object of the present invention to provide a construction for the securing of heat insulation to a concrete roof structure which is less liable to damage as aforesaid.